The Cylinder Head, Valves and Valve Gear

Abstract

It has been shown how the point of detonation for a petrol is dependent on the compression ratio and the shape of the combustion chamber, and that it is desirable to use the highest possible compression ratio. To avoid detonation and pre-ignition, a compact combustion chamber and a short flame path are desirable. The shape and dimensions of the chamber are governed partially by the valve size and the cost of manufacture. A short flame path may be gained by causing the charge to travel towards the plug during the burning period, by careful design of the cylinder head to direct the flow of charge and by bringing the piston very close to the head at suitable points to squeeze the gas out of the small volume left in the direction of the plug. The area that does this is known as a squish band.